Preparation of thermoset cycloolefin polymers by the ring opening metathesis polymerization (ROMP) is a relatively recent development in the polymer art. Reaction injection molding (RIM) of polyolefins by the ring-opening of metathesis polymerizable polycyclic olefinic monomers in the presence of alkylidene complexes is a particularly important aspect of polycyclic olefin chemistry. For example, Klosiewicz (U.S. Pat. Nos. 4,400,340 and 4,520,181) discusses a method whereby polydicyclopentadiene can be prepared by combining a plurality of reactant monomer streams. Klosiewicz discloses the preparation of ROMP polymers from dicyclopentadiene via a two-stream reaction injection molding technique wherein one stream, includes a “procatalyst”, and the second stream, includes a “procatalyst activator” or “activator”. The monomer reactant streams are combined in a mix head where the procatalyst and activator generate an active metathesis catalyst. The reactive catalyst/monomer mixture is immediately injected into a mold where, within a matter of seconds, polymerization takes place forming a solid article in the shape of the mold. Although such metathesis catalysts are very effective in the polymerization of polycyclic olefins, the unsaturated nature of the starting monomers is retained in the polymer backbone. In addition, the resultant polymer contains a repeat unit with one less cyclic unit than did the starting monomer as shown in the reaction scheme below. In sharp contrast, despite being formed from the same monomer, an addition-polymerized polycyclic olefin is clearly distinguishable over a ROMP polymer. Because of the different (addition) mechanism, the addition polymer has no backbone C═C unsaturation as shown in the reaction scheme below. 
The difference in structures of ROMP and addition polymers of polycyclic monomers is evidenced in their properties, e.g., thermal properties, mechanical properties after aging, and polymer surface quality. The addition-type polymer of polycyclic olefins such as norbornene has a high Tg of about 350° C. The unsaturated ROMP polymer of norbornene exhibits a Tg of about 35° C., and exhibits poor thermal stability at high temperature above 200° C. because of its high degree of backbone unsaturation.
Ring-opened metathesis polymers and copolymers of dicyclopentadiene are known to have excellent glass transition temperatures (Tg) and high impact resistance. Because of their high Tg values, however, these polymers are difficult to melt process once formed. Crosslinking in the melt also occurs when the ring-opened polymer or copolymer contains a pendant five member unsaturated ring such as results when dicyclopentadiene is used to form the polymer or copolymer. Crosslinked polymers are extremely difficult to melt process. This poses a significant disadvantage to solution polymerized polymers which must be melt processed to provide finished articles. In contrast, for polymers and copolymers prepared in bulk, processing, in terms of melt flow, is less of a problem since the polymerization takes place in a mold and in the shape desired. Melt processing for such bulk polymerized polymers and copolymers is normally not required. Therefore, bulk polymerization provides significant advantages where high temperature resistance is desired in the finished article.
Suld, Schneider, and Myers (U.S. Pat. No. 4,100,338) disclose a method to polymerize norbornadiene to a solid polymer in the presence of a catalytic system of nickel acetylacetonate or a nickel-phosphine complex and an alkyl aluminum chloride. They note that if the temperature increases too much then cooling is required to successfully polymerize the monomer. Typically, polynorbornadiene is processed at temperatures of less than 100° C. Generally, however, the polymerization of the norbornadiene with an optimal amount of the catalyst system is not characterized by a rapid exotherm.
In similar fashion, Brownscombe and Willis (U.S. Pat. No. 4,451,633) polymerized an olefinic monomer feed in the presence of a Ziegler-Natta type coordination catalyst system comprising a Group IV metal containing component and activator hydrides and halides, an organometal activator selected from Groups I to III. This method permits the production of polyolefinic articles that are difficult or impossible to produce from polyolefinic powder or pellets by convention methods. The monomer feed in U.S. Pat. No. 4,451,633 comprises aliphatic and cycloaliphatic alpha olefins as well as other diolefins (producing polymeric articles containing some unsaturation).
Polymers having improved heat resistance can be obtained through the use of comonomers. For example, the heat resistance of dicyclopentadiene can be increased by copolymerizing DCPD with a crosslinking or bulky comonomer. However, the improved heat resistance obtained at the cost of decreased impact resistance.
Sjardijn and Snel (U.S. Pat. No. 5,093,441) employed ring-opening metathesis polymerization on specifically bulky norbornenes (generated from the 1:1 Diels-Alder adducts of cyclopentadiene and norbornene, norbornadiene and cyclooctadiene) to provide copolymers showing tailored properties, such as increased glass transition temperature. Likewise, Hara, Endo, and Mera (European Patent Application No. 287762 A2) prepared highly crosslinked copolymers by metathesis from heat treated cyclooctadiene and dicyclooctadiene.
Tsukamoto and Endo (Japanese Patent Application, 9-188714, 1997) polymerized ethylidene norbornene via Ziegler type polymerization in a RIM process to yield addition polymerized solid objects. The disclosed catalyst comprise a Group IV metal containing procatalyst and Group III metal containing activator.
Nagaoka et. al. (Japanese Published Application No. 8-325329, 1996) describe a process for the polymerization of a polycycloolefin polymer via reaction injection molding (RIM) in the presence of a Group 10 transition metal compound and a cocatalyst. A molded article containing no unsaturated bonds is polymerized from norbornene-type monomers containing only one polymerizable norbornene functionality. There is no disclosure or suggestion of a crosslinked polymer product or a procatalyst species containing both a Group 15 electron donating ligand (e.g., triphenylphosphine) and a hydrocarbyl ligand that are coordinated to the Group 10 metal. The co-catalyst species are selected from a myriad of compounds including organoaluminums, Lewis acids, and various borate salts. The use of simple Group 1, Group 2 and transition metal salts are not discussed or exemplified. Accordingly, a Group 10 metal catalytic species that requires the presence of both a Group 15 electron donating ligand and a hydrocarbyl ligand are not contemplated. In addition, there is no suggestion, implication, or teaching of the important combination of a Group 10 metal procatalyst containing a Group 15 electron donor ligand and a hydrocarbyl ligand in combination with a weakly coordinating anion salt activator.
Goodall et al. (U.S. Pat. Nos. 5,705,503; 5,571,881; 5,569,730; and 5,46,819) have shown that Group 10 catalyst systems are useful in generating thermoplastic addition polymers from a variety of norbornene derivatives in polar and non-polar solvents. The catalyst system employs a Group 10 metal ion source, a Lewis acid, an organoaluminum compound, and a weakly coordinating anion. The glass transition temperature of the polymers are in the range of 150° C. to 350° C. In the absence of a “chain transfer agents” polynorbornene polymers are generated whose molecular weights (Mw) are over 1,000,000. Polymers formed with too low a molecular weight are of limited utility in thermoplastic articles. Polymers with too high a molecular weight can only be cast from solution and in some cases are completely insoluble and difficult to thermoform. “Melt-processable” means that the polymer is adequately flowable to be thermoformed in a temperature window above its Tg, but below its decomposition temperature. There is no disclosure of a method to directly polymerize a polycyclic olefinic monomer directly into a polymeric article of manufacture.
Thermoset polymers with high impact strength and high modulus find useful applications as engineering polymers in such articles of manufacture as automobiles, containers, appliances, recreational equipment, and pipe.
Any good thermoset polymer should meet at least two criteria. It should have desirable physical properties and it should lend itself to easy synthesis and forming. Among the most desirable physical properties for many polymers is a combination of high impact strength, high temperature performance, and high modulus. A standard test for impact strength is the notched Izod impact test, ASTM No. D-256. For an unreinforced thermoset polymer to have good impact strength, its notched Izod impact should be at least 1.5 ft. lb./in. notch. It is desirable that this good impact strength be combined with a modulus of at least about 150,000 psi at ambient temperature. Among the critical factors in the synthesis and forming of a thermoset polymer are the conditions required to make the polymer set up or gel. Many thermoset polymers require considerable time, elevated temperature and pressure, or additional steps after the reactants are mixed before the setting is complete.
Not only is it desirable that the thermoset polymer have high impact strength, but it is also desirable that it be easily synthesized and formed. A RIM process achieves this second goal by in-mold polymerization. The process involves the mixing of two or more low viscosity reactive streams. The combined streams are then injected into a mold where they quickly set up into a solid infusible mass. RIM is especially suited for molding large intricate objects rapidly and in low cost equipment. Because the process requires only low pressures, the molds are inexpensive and easily changed. Furthermore, since the initial materials have low viscosity, massive extruders and molds are not necessary and energy requirements are minimal compared to the injection molding or compression molding commonly used.
For a RIM system to be of use with a particular polymer, certain requirements must be met: (1) The individual streams must be stable and must have a reasonable shelf life under ambient conditions. (2) It must be possible to mix the streams thoroughly without their setting up in the mixing head. (3) When injected into the mold, the materials must set up to a solid system rapidly. (4) Any additives (i.e., fillers, stabilizers, pigments, etc.) must be added before the material sets up. Therefore, the additives selected must not interfere with the polymerization reaction.
It can be seen that when developing a RIM process a tradeoff must be made. It is desirable that the polymer set up quickly, but the polymerization cannot be too quick. The components cannot be so reactive that they set up in the mixing head before they can be injected into the mold. Once in the mold, however, the polymer should set up as quickly as possible. It is not desirable that the polymer take a long time or require additional steps to gel completely.
There is an interest in stabilizing Group 10 transition metal cationic catalysts with anionic species. It would be desirable to provide a catalyst for the polymerization of norbornene, other hydrocarbon polycyclic olefins and crosslinkable polycyclic olefins, and norbornenes bearing functional groups. In particular, it is desirous to develop weakly coordinating anions which are stable at a wide variety of temperatures, resistant to impurities, not hazardous to make or use, inexpensive, and capable of being used with a wide a variety of monomers and solvents, including those with functional groups. One very desirable attribute is hydrocarbon solubility for both the cation weakly coordinating anion pair activator as well as the resultant Group 10 transition metal cationic catalyst.
There is a need for polycyclic olefinic polymers that have very low levels of residual monomer, no solvent, higher levels of heat resistance, and resistance to oxidation and degradation, while maintaining other properties, such as impact and tensile strengths at levels similar to those found in the prior art. In the case of dicyclopentadiene polymerization, if the reaction is not virtually quantitative, there will be unreacted monomer in the thermoset product and the molded article will have an undesirable odor. This odor greatly limits the applications in which polymerized product can be used.
Highly converted, crosslinked, and toughened polyolefinic articles have not been produced by carrying out the addition polymerization of a polycyclic monomer with a coordination catalyst in a mold having the shape of the desired article.